Brake control system

ABSTRACT

An antiwheel-lock brake control system in which, following the detection of incipient wheel lock, brake apply pressure is initially relieved and thereafter controlled by cyclical time duration modulation of an operator-initiated brake apply pressure.

United States Patent [191 Neisch July 3, 1973 [54] BRAKE CONTROL SYSTEM 3,620,577 ll/l97l Neisch et al. 303]? X [75] Inventor: James C. Neisch, Orchard Lake,

Primary Examiner-Allen N. Knowles [73] Assignee: North American Rockwell Assistant Examiner-Gene A. Church Corporation, Pittsburgh, Pa. Attorney-John R. Bronaugh et al. [22] Filed: Jan. 3, 1972 [2]] Appl. No.: 214,793

[5 7] ABSTRACT [52] US. Cl 303/21 F, 188/181 A [51] Int. Cl B60t 8/06 An antiwheel-lock brake control system in which, fol- -[58] Field of Search 303/2] F, 40, 7; lowing the detection of incipient wheel lock, brake 188/181 A apply pressure is initially relieved and thereafter controlled by cyclical time duration modulation of an oper- [56] 7 References Cited ator-initiated brake apply pressure.

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TIME

BRAKE CONTROL SYSTEM BACKGROUND AND SUMMARY OF INVENTION In earlier forms of antiwheel-lock brake control systems, it was proposed to terminate normal brake pressure application after detection of incipient wheel lock and thereafter to alternately connect and disconnect the fluid pressure actuated brake to and from the pressure source. This was referred to as pulsing the brakes. In systems such as these, the on and off times of the pulser were equal and of fixed duration and,as a result, the apply pressure actually delivered to the brake actuators ultimately reached some resultant pressure level lower than the original apply pressure level. U.S. Pat. No. 3,503,654, issued Mar. 31, 1971 to A. F. Stamm for Brake System illustrates several brake systems operating on this principal. Later it was proposed to provide an antiwheel-lock brake control system in which, following detection of incipient wheel lock, various pressures levels could be applied to the brake actuators, depending upon the changes in wheel velocity detected.The system illustrated in U.S. Pat. No. 3,602,553, issued Aug. 31, 1971 to James C. Cumming and James C. Neisch for Brake System is an example of this later development. An analysis of the problem of minimizing stopping distance and maintaining lateral stability of the vehicle during braking under adverse conditions continued and asgovernmental limitations on stopping distance and lateral vehicle motion become more stringent, it became apparent that a greater variety of pressure levels at the brake actuators was necessary. This has led to the development of the so-called adaptive systems of brake control.

The present invention provides an improved system of brake pressure control in which the theoretically infinite number of discrete levels of pressure delivered to the brake actuator can be automatically selected dependent upon the various influences existing at any given time, such as the coefficient of friction between each of the wheels and the road, the angular velocity of each of the wheels, the rate of deceleration of each of the wheels, etc.

More specifically, the present invention provides a novel system, both method and apparatus, in which, upon detection of incipient wheel lock, the brake apply pressure is rapidly reduced and thereafter, in dependence upon the changes in velocity of the associated wheel or wheels, full apply pressure is gradually restored in stages by cyclical time duration modulation of operator-initiated brake apply pressure. Within any given cycle (40 ms. for example) the duration in which the operator-initiated brake apply pressure is effective to tend to increase the pressure at the brake actuator can vary from zero milliseconds to the full duration (i.e., 40 m.s.) of the cycle. Any number of discrete steps between these extremes can be provided. For example, if a cycle is divided into ten equal segments, the I on time, that is the time during which the operatorinitiated brake apply pressure is connected to tend to increase thepressure at the brake actuator, can be selected in any of the increments. A lesser or greater number of increments can be provided as required.

As a further important characteristic of this invention, in the event of failure of the electrical wheel lock detection system, the brake application system remains normally operative. This is achieved by providing a normally open solenoid-operated valve in the fluid connection through which the vehicle operatorinitiated brake apply pressure is effective. So long as the solenoid is deenergized, the brake apply pressure is on.

THE DRAWINGS FIG. 1 is a diagrammatic illustration of a typical installation of the present invention;

FIG. 2 is a central vertical section illustrating details of construction of one embodiment of a valve useful in the present invention;

FIG. 3 is a fragmentary section showing components of the valve of FIG. 2 in a different operating position;

FIG. 4 is a vertical section showing the details of another embodiment of a valve useful in the present invention;

FIG. 5 is a vertical section rotated from the section of FIG. 4 and showing components of the valve in a different operation position; and

FIG. 6 is a chart illustrating time pressure curves under typical conditions. 7

Referring now more particularly to FIG. 1, in the present invention a single control valve is preferably utilized to control the brake on all wheels mounted on one axle. In the illustrated embodiment, one of the control valve assemblies, indicated generally at 20, controls the operation of the paired actuators 22-23 and 24-25 associated with brake mechanisms 26 and 27 of the wheels on the front axle 283. An identical control valve assembly 20 controls the paired actuators 29-30 and 31-32 associated with the brake mechanisms 33 and 34 on the rear vehicle axle 35. Valve assemblies 20 and 20' are mounted on the axles 28 and 35 by brackets (not shown).

The remainder of the brake system includes the usual compressor 36 which delivers air under pressure to a supply reservoir 37 and thence to series connected service reservoirs 38 and 39, the former being connected to supply air under service pressure, for example, psi, through line 41 to the control valve 20 associated with the front axle and the latter being connected to supply service air through line 41' to the control valve 20' associated with the rear axle.

The service reservoir 38 is also connected to supply air under pressure to the usual treadle valve 40. When the operator depresses the treadle valve 40, air under the selected pressure is delivered to the control chambers of the control valves 20 and 20' through lines 42 and 42', respectively, as \explained in detail below. When the treadle valve is released, it vents the pressure in the control chamber. i

The electrical control system, which controls the action of the valves 20 and 20', is preferably of the form disclosed in copending application, Ser. No. 268,070, Filed June 30, 1972 (NR Case 1932) and owned by ap plicants assignee. Briefly, the system includes sensors 44 mounted on the axles 28 and 35 adjacent notched discs 46 rotatable with each of the wheels, the sensors 44 generating signals indicative of the angular velocity of the wheels. These signals from the sensors 44 for each axle are supplied to a computer unit carried by the housing of the valves 20 and 20 for that axle. The velocity signals are processed and under certain conditions actuate the valves to modify the brake pressure applied by the operator through the treadle valve 40 in a manner explained in greater detail below.

Referring now more particularly to FIG. 2, the valve assembly 20 includes a main, generally cylindrical body member 52 having an inlet opening 54 to which air is supplied from the reservoirs 38 or 39 through line 41 or 41' and having one or more outlet openings 56 (one shown) for supplying air to the brake actuators through the lines 57 or 57. The housing also has a pair of vent openings 58 and 60, the former covered by a filter 62 and the latter being formed in a fitting 64 threaded into the base of the main housing 52.

Secured to the upper end of the main housing 52 by a plurality of bolts (not shown) is an upper housing 66 having a laterally extending cavity 68 which houses a solenoid coil 70 and is closed by an end cover plate 72. A housing 73 detachably secured to the lower end of main housing 52 encloses and supports a computer 75 which processes the signals from the sensors 44 and controls the solenoid 70 as more fully explained in the aforesaid copending application.

Clamped between the main housing 52 and the upper housing 66 is a flexible diaphragm 74 which separates the main flow chamber 76 in the housing 52 from a control chamber 78 in the upper housing 66. The diaphragm 74 also acts as a valve member selectively connecting and disconnecting the flow chamber 76 and an annular chamber 80 communicating with the vent passage 58.

The lower surface of diaphragm 74 is supported on the upper surface of a piston 82 mounted for limited vertical reciprocation in the flow chamber 76. The piston 82 is slidably mounted on the upper end of a stem 84, the lower portion of which carries a valve member 86 having an annular sealing member 88 adapted to engage an annular seat 90 to selectively open and close a passage 92 connecting the inlet 54 with the flow chamber 76.

The lower portion of the valve member 86 is slidably received in a fitting'94 threaded into the valve body 52. A spring 96 compresses between the fitting 94 and the valve 86 urges the latter toward closed position. To permit free movement of the valve 86 in the fitting 94, the internal space between the parts is vented through a stem passage 98. To facilitate installation and removal of the fitting and valve body 86 as a unit the parts are preferably held in assembled relation by a lock ring 100.

The flow chamber 76 is connected to a quick release valve chamber 102 through a passage 104. A quick release valve assembly comprises a valve plate 106 urged by spring 108 to the position shown to open the vent passage 60, thus venting the brake actuators. When the brakes are applied, the pressure developed in chambers 76 and 102 moves the valve plate 106 downwardly from the position shown to close the vent opening 60 and permit free communication between the flow chamber 76 and the brake actuators.

The pressure in control chamber 78 is regulated by a shuttle valve or plunger 110 slidably received in a fitting 1 12, an extension of which passes through the central aperture of the solenoid coil 70. The shuttle valve 110 is normally biased to the left by spring 114 to close a vent port 116 as shown in FIG. 2. When the shuttle valve is in this position, air from the treadle valve 40 passes through a central aperture 118 in fitting 120 and along flutes 121 in the valve plunger 110 into passage 122, then into the control chamber 78. When the solenoid 70 is energized, the valve plunger 110 is magentically attracted and thus moves to its opposite limit position, closing the end of passage 118 and connecting the control chamber 78 to the atmosphere through the passage 122 and the vent port 116 as shown in FIG. 3.

The valve is shown in FIG. 2 in its brake OFF position. Air under full service pressure, for example, psi, is supplied to the upstream side of the valve 86, which maintains the port or passage 92 closed because of the pressure differential across the valve augmented by the action of the spring 96. Accordingly, all other portions of the valve are under essentially atmospheric pressure and the brakes are fully released. When the operator actuates the treadle valve 40, air under pressure determined by the operator selected-position of the treadle valve is supplied through line 42 or 42' to the control chamber 78. The establishment of the selected pressure in the control chamber 78 depresses diaphragm 74 and piston 82 to open valve 86, permitting air to flow from the inlet port 54 through the port 92 and the passage 104 to move the valve plate 106 downwardly to its seated position permitting the passage of air through the port 56 to the brake actuators. At this time, the pressure differential across the diaphragm also maintains the annular exhaust chamber 80 isolated from the flow chamber 76.

As soon as the brakes are seated, the pressure in the brake line and the flow chamber 76 repidly increases until the pressure differential across the diaphragm 74 is eliminated thus restoring the piston 82 and the diaphragm to their original neutral or balanced positions, permitting valve 86 to close, thus establishing the pressure at the brake actuators in accordance with that selected by the operator. When the operator releases the treadle vavle 40, the pressure in the supply lines 42, 42' and the pressure in control chamber 78 is reduced to atmospheric. The pressure in flow chamber 76 is supplied to the underside of the diaphragm 74 through one or more vent openings 123, which lifts the diaphragm off the annular seat 124 to connect the control chamber and the space above the valve plate 106 to atmosphere through the vent port 58 as shown in FIG. 3. The valve plate 106 is immediately lifted from its seat by spring 108, venting the brake actuators.

The operation of the valve thus far described assumes that the operator did not supply sufficient brake pressure to cause the wheels to exceed acceptable slip. When excessive slip occurs, the control system (including sensors 44 and computer 75) with which the valve is associated generates two types of signals. The first signal calls for complete brake release to permit the wheels to regain synchronous speed. The control system also generates signals calling for partial brake ap plication pressure after the wheels begin to accelerate. The brake OFF signal energizes the solenoid 70 and maintains the solenoid energized as long as the signal persists. The partial brake pressure signal,'on the other hand, rapidly cycles the solenoid on and off.

When the brakes are applied initially, the valve will function in the manner thus far described until the brake OFF signal is generated. When this occurs, the energization of the solenoid 70 will shift the plunger to the right, (FIG. 3) closing the inner end of port 118 and opening the vent port 116. This reduces the pressure in control chamber 78 essentially to atmospheric pressure, and the consequent action of the valve is the same as if the treadle valve had been released, producing essentially immediate release of the brakes.

If the brake OFF signal is discontinued, the solenoid 70 is deenergized, permitting the plunger 110 to move to the left as viewed in FIG. 2 under the influence of fluid pressure differential and force of the spring 114, closing the vent port 116, opening the inlet port 118, and permitting the development in the control chamber 78 of the pressure signalled by the vehicle operator, thus again placing the brakes under full operator control.

Usually the control system described in the aforementioned copending application is effective, upon the detection of an actual or incipient skid condition, to produce a signal calling for brake release followed by a signal calling for partial brake application at a preselected level or a series of preselected levels. The signal is such as to control the duty cycle of the solenoid 70. More specifically, the signaal controls the ratio of solenoid ON time to solenoid OFF time in a series of relatively short discrete time intervals. In a typical case the basic cycle time is 40 msec. To establish the desired level of brake pressure, the control system energizes the solenoid 70 during a predetermined fraction of each 40 msec period. As the ratio of ON time to OFF time in each cycleperiod is increased, the brake pressure is reduced. I

The rapid cycling of the solenoid places the plunger 110 in which may be-called adithering' mode, in which the plunger rapidly moves between the limit positions shown in FIGS. 2 and 3 in which the control chamber 78 is connected to pressure and to exhaust, respectively. I

The performance of the control valve under these conditions is illustrated by the graph FIG. 6. In this example it is assumed that a brake OFF signal has been generated reducing the pressure in control chamber 78 and the pressure in the brake actuators essentially to atmospheric, that the service pressure supplied to the inlet port 118 through the lines 42 or 42 is 100 psi, and that it is desired to establish a duty cycle for the solenoid 70 such that the ratio of ON time to OFF time is 3:1; that is, OFF time is 25 percent of the total cycle time.

In the first 40 msec interval, the pressure in control chamber 78 will rise relatively rapidly because of the high pressure differential between the pressure existing at inlet opening 118 and the pressure then existing in control chamber 78. During the solenoid ON time, the control chamber 78 is vented, but the pressure decay rate is relatively small because of the relatively low pressure differential between the control chamber and the atmosphere. In the succeeding cycles the rate of pressure increase during each solenoid OFF period will decrease and the rate of pressure decay during solenoid ON period will decrease. As the pressure differential between the inlet-opening 118 and the control chamber decreases and the pressure differential between the pressure in the control chamber 78 and atmosphere increases, eventually the pressure in control chamber 78 will reach equilibrium value at approximately 25 psi. The pressure in flow chamber 78 and the pressure to brake actuators will follow the pressure in control chamber 78 as explained above.

It will be apparent that by increasing the ratio of ON time to OFF time, the system will reach equilibrium at a lower pressure and, conversely, by decreasing the ratio of ON time to OFF time, the system will reach equilibrium at a higher pressure.

FIGS. 4 and 5, to which detailed reference will now be made, illustrate another embodiment of the valve in accordance with the present invention, the action of which is essentially the same as the action of the embodiment described above. 7

The main valve body has an inlet opening 132 for connection to the service reservoirs 38 or 39 through line 41 or 41' and an outlet opening 134 connected to the brake actuators through lines 57 or 57'. The pe riphery of a diaphragm 136 divides the valve into a control chamber 148 and a flow chamber 150.

A double valve assembly 152 is mounted for vertical reciprocation on a fixed stem 154 carried by a bottom cover plate 156 suitably secured to the valve body 130. The valve has an upper seal 158 adapted to engage an annular seat 160 formed on the sleeve 144 and a lower seal 162 adapted to engage an annular seat 164 formed on a sleeve 166, the lower end of which is clamped against the body 130 by the bottom cover plate 156.

The stem 154 has a series of longitudinally extending flutes or serrations 167 to connect the space below the valve assembly 152 with the interior of the sleeve 144 and the boss 146, the upper end of which is vented to the atmosphere through a filter 168 and a protective cover plate 170.

The cover plate 138 is provided with a laterally projecting housing 172 containing a solenoid 174 and a plunger 176 which is biased by spring 178 to the position shown to block a vent port 180 leading to the interior of the boss 146 and to permit the flow of air under pressure from the treadle valve through inlet port 182 and passage 184 into the control chamber 148.

When the solenoid 174 is energized, the plunger 176 moves to its opposite limit position to block the inlet port 182 and connect the control chamber to atmosphere through the port 180 as :in the previously described embodiment.

As shown in FIG. 5, the cover 138 is provided with a second housing 186 circumferentially spaced from the housing 172. The housing 186, which is closed by y a removably cover plate 188, houses the computer 190, which receives the signals from the sensors 44 and controls the solenoid 174.

The valve is illustrated in FIG. 4 in the brake OFF position. The flow of air under pressure into the valve is blocked by the engagement of seal 162 with the seat 164. The flow chamber and the cotnrol chamber 148 are under atmospheric pressure. During normal brake application, air under pressure is transmitted through the treadle valve 40 directly to the control chamber through lines 42 or 42' to inlet passage 182 and passage 184. The pressure dlifferential across the diaphragm 136 will depress the diaphragm tightly engaging seal 158 and seat moving the valve assembly 152 downwardly against the action of spring 192 to permit air under pressure to enter flow chamber 150 and pass through the opening 194 and through the outlet port 134 to the brake actuators. As soon as the pressure in the flow chamber 150 equals the pressure in the control chamber 148, the components of the valve will resume the neutral or balanced position shown in FIG. 4.

When the operator discontinues the application of brakes at the treadle valve 40, the pressure in the control chamber 148 is rapidly reduced to atmospheric, and the resulting upwardly acting; pressure differential across the diaphragm 136 will lift the diaphragm and move the valve seat 160 away from side 158 as shown in FIG. 5, thus connecting chamber 150, port 134, and the brake actuators to exhaust through the passage in the boss 146.

The action of the solenoid 174 in releasing the brakes when energized or in establishing a partial brake pressure when cyclically energized and deenergized is the same as in the previously described embodiment.

What is claimed is:

l. A method of operating an antiwheel-lock braking system of the type which includes a vehicle operatorcontrolled fluid control pressure generator, a brake actuating fluid pressure source, a fluid pressureresponsive brake actuator, a main valve connected to said fluid pressure source and having a discharge passage from which brake actuating pressure is supplied to said brake actuator, and a control device responsive to the control pressure from said generator and operatively connected to said main valve for controlling the application of brake actuating pressure to said brake actuator, the method comprising the steps of actuating the generator to actuate the fluid pressure control device to cause said main valve to apply brake actuating pressure to the brake actuator, operating said fluid pressure control device to rapidly, termporarily relieve the brake actuating pressure applied to the brake actuator and temporarily terminating connection of the generator output pressure to said fluid pressure control devcie independently of said pressure generator, cycylically reconnecting and disconnecting said fluid pressure control device to and from the generator output pressure, whereby a desired magnitude of fluid pressure is established at the brake actuator by varying the relative magnitude of the durations of the connection and disconnection of the fluid pressure control device and the generator during successive cycles.

2. The method defined in claim 1 further comprising the steps of gradually increasing the duration of the connection time relative to the disconnection time to thereby gradually increase the magnitude of fluid pressure at the brake actuator.

3. An antiwheel-lock braking system comprising: a vehicle operatoncontrolled fluid control pressure generator, a brake actuating fluid pressure source, a fluid pressure-responsive brake actuator, a main valve connected to said fluid pressure source and having a discharge passage from which brake actuating pressure is supplied to said brake actuator, a control device responsive-to the control pressure from said generator and operatively connected to said main valve for controlling the application of brake actuating pressure to said brake actuator, means for operating said fluid pressure control device to rapidly, temporarily relieve the brake actuating pressure applied to the brake actuator and temporarily terminating connection of the generator output pressure to said fluid pressure control device independently of the operation of said pressure generator, said operation means including means for cyclically reconnecting and disconnecting said fluid pressure control device to and from the output of said generator, whereby a desired magnitude of fluid pressure is established at the brake actuator by varying the relative magnitude of the durations of the connection and disconnection of the fluid pressure control device and the generator.

4. The braking system defined in claim 3, wherein said operating means includes a solenoid actuated valve interposed in a fluid conduit between said control device and said operator-controlled generator, and said solenoid is cyclically energized and deenergized to disconnect and reconnect said control device from said generator.

5. The system defined in claim 4, wherein said solenoid actuated valve is normally biased mechanically to its open position providing direct fluid communication between said operator-controlled generator and said control device, whereby, in the event of operational failure of said solenoid the system will operate in its normal manner but without its antiwheellock function. 

1. A method of operating an antiwheel-lock braking system of the type which includes a vehicle operator-controlled fluid control pressure generator, a brake actuating fluid pressure source, a fluid pressure-responsive brake actuator, a main valve connected to said fluid pressure source and having a discharge passage from which brake actuating pressure is supplied to said brake actuator, and a control device responsive to the control pressure from said generator and operatively connected to said main valve for controlling the application of brake actuating pressure to said brake actuator, the method comprising the steps of actuating the generator to actuate the fluid pressure control device to cause said main valve to apply brake actuating pressure to the brake actuator, operating said fluid pressure control device to rapidly, termporarily relieve the brake actuating pressure applied to the brake actuator and temporarily terminating connection of the generator output pressure to said fluid pressure control device independently of said pressure generator, cycylically reconnecting and disconnecting said fluid pressure control device to and from the generator output pressure, whereby a desired magnitude of fluid pressure is established at the brake actuator by varying the relative magnitude of the durations of the connection and disconnection of the fluid pressure control device and the generator during successive cycles.
 2. The method defined in claim 1 further comprising the steps of gradually increasing the duration of the connection time relative to the disconnection time to thereby gradually increase the magnitude of fluid pressure at the brake actuator.
 3. An antiwheel-lock braking system comprising: a vehicle operator-controlled fluid control pressure generator, a brake actuating fluid pressure source, a fluid pressure-responsive brake actuator, a main valve connected to said fluid pressure source and having a discharge passage from which brake actuating pressure is supplied to said brake actuator, a control device responsive to the control pressure from said generator and operatively connected to said main valve for controlling the application of brake actuating pressure to said brake actuator, means for operating said fluid pressure control device to rapidly, temporarily relieve the brake actuating pressure applied to the brake actuator and temporarily terminating connection of the generator output pressure to said fluid pressure control device independently of the operation of said pressure generator, said operating means including means for cyclically reconnecting and disconnecting said fluid pressure control device to and from the output of said generator, whereby a desired magnitude of fluid pressure is established at the brake actuator by varying the relative magnitude of the durations of the connection and disconnection of the fluid pressure control device and the generator.
 4. The braking system defined in claim 3, wherein said operating means includes a solenoid actuated valve interposed in a fluid conduit between said control device and said operator-controlled generator, and said solenoid is cyclically energized and deenergized to disconnect and reconnect said control device from said generator.
 5. The system defined in claim 4, wherein said solenoid actuated valve is normally biased mechanically to its open position providing direct fluid communication between said operator-controlled generator and said control device, whereby, in the event of operational failure of said solenoid the system will operate in its normal manner but without its antiwheel-lock function. 